This invention relates to components comprised of abrasive compacts. Typical areas of application for such components are in wire dies, wear surfaces, rock cutting and drilling equipment and cutting tools for machining. The area of primary interest for this invention is in components useful as cutters for rock drilling bits and techniques for fabrications of such components.
A cluster compact is defined as a cluster of abrasive particles bonded together either (1) in a self-bonded relationship, (2) a means of a bonding medium disposed between the crystals, or (3) by means of some combination of (1) and (2). Reference can be made to U.S. Pat. No. 3,136,614, U.S. Pat. No. 3,233,988 and U.S. Pat. No. 3,690,818 for a detailed disclosure of certain types of compacts and methods for making same. (The disclosures of these patents are hereby incorporated by reference herein.)
A composite compact is defined as a cluster compact bonded to a substrate material such as cemented tungsten carbide. A bond to the substrate can be formed either during or subsequent to the formation of the cluster compact. Reference can be made to U.S. Pat. Nos. 3,743,489, 3,745,623 and 3,767,371 for a detailed disclosure of certain types of composite compacts and methods for making same. (The disclosure of these patents are hereby incorporated by reference herein.)
Brazing is defined as a group of welding processes wherein coalescense is produced by heating to suitable temperatures above 800.degree. F. and by using a brazing filler metal having a melting point below that of the base metals. The filler metal is distributed between the closely fitted surfaces of the joint by capillary action.
Filler metal is defined as brazing filler metals and other metals or alloys used in bonding techniques such as diffusion bonding, hot pressing, resistance welding and the like. The filler may be either added as an additional component to the metal parts being bonded or formed from the metals of the parts themselves (e.g., fusion welding as defined in Van Nostrand's Scientific Encyclopedia, Fifth Edition (1976) pp 2330-2331).
A brazing filler metal is defined as a metal or alloy to be added when making a braze and having melting temperature above 800.degree. F. (but below those of the metals being joined).
Conventional rotary drill bits for oil and gas well drilling and core drilling have heretofore used cutting elements such as (1) steel teeth, (2) steel teeth laminated with tungsten carbide, (3) an insert of cemented tungsten carbide, and (4) natural diamonds, all of which are set or molded in a tungsten carbide crown or cone. Due to the relatively short life and/or high operating cost of these conventional designs, it has recently been proposed to use synthetic diamond composite compacts as the cutting element in such drills.
In adapting composite compacts to certain drill bit applications, it has been found to be desirable to provide an elongated base or support for the composite compact to aid in attachment in the drill crown. While it is technically feasible to form an integral composite compact of an adequate length directly under high temperature and pressure, as disclosed in application Ser. No. 699,411 cross referenced above, this has not as yet been adopted commercially because of the significantly increased cost of manufacture. This becomes clear when realizing that the capacity of the reaction cell in which the compacts are made, under high temperatures and pressures, is limited. Thus, if compacts were produced as suggested in application Ser. No. 699,411, the number of compacts produced per cell would be reduced by about one-half potentially making the cost prohibitive.
One approach to avoiding this added cost is to braze an additional length of cemented carbide to the carbide base of the composite compact as disclosed in application Ser. Nos. 746,044 and 796,635 cross referenced above.
In field tests of these latter two designs, one problem which has been encountered is that the stresses on each cutting element are severe and some disattachment of the cutters has been encountered. The stresses are caused because the structure of most rocks is heterogeneous and thus have layers of varying hardness. These layers cause large variations in the impact loads applied to the cutting elements during drilling, and the bond strength of such designs is not always strong enough to withstand this.
In these designs, available attachment techniques and acceptable brazing filler metals for use with a diamond composite compact made in accordance with the teaching of U.S. Pat. No. 3,745,623 were limited because the diamond layer of such compacts is thermally degraded at temperatures above approximately 700.degree. C. Similarly, it has been found that a cubic boron nitride (CBN) composite compact made in accordance with the teaching of U.S. Pat. No. 3,743,489 is also thermally degraded at temperatures above approximately 700.degree. C. Because of the thermal degradation problem, it has been necessary to use brazing filler metals with a liquidus below 700.degree. C. Such metals form brazing joints generally of lower strength than braze filler metals having a higher liquidus. Even when the lower temperature liquidus metals (such as BAg-1-ASW-ASTM classification) are used, temperatures approaching those at which the diamond layer is degraded are required; hence, great care is required to prevent degradation of the compact during brazing.
Accordingly, it is an object of this invention to provide improved and stronger components comprised of composite compacts.
Another object of this invention is to provide an improved cutter component for drill bits.
Another object of this invention is to provide an improved fabrication technique for forming high strength bonds to composite compacts without degrading the particulate layer of the composite compact.
Another object of this invention is to provide an improved fabrication technique for forming a high strength bond between a composite compact and cemented carbide pin in the fabrication of cutters for drill bits.
Another object of this invention is to provide improved techniques whereby small composite compacts produced by an expensive high temperature, high pressure process can be dimensionally scaled up to larger sizes permitting easier attachment of the compact to a tool body.